Industrial processing plants use control valves in a wide variety of applications from controlling process flow in petroleum refineries to maintaining fluid levels in tank farms. Control valves, which are typically automated, are used to manage such fluid flow by functioning like a variable orifice or passage. By controlling an internal valve component, such as a valve plug, the amount of product passing through the valve body can be accurately regulated. The control valve is typically automated using a pressure-operated actuator that is controlled by a remotely-operated field instrument. The field instrument communicates with a process control computer to command fluid flow changes within the valve to achieve the plant operators' desired control strategy via pressure-operated actuators. Electropneumatic converters, such as current-to-pressure transducers, are in common use in field instruments to provide a conversion of an electrical signal to a volumetric flow or pressure output to control the actuator and, therefore, the control valve.
Current electropneumatic converters either provide continuous, proportional current-to-pressure conversion or provide intermittent or pulsed-mode current-to-pressure conversion. Existing continuous conversion electropneumatic converters consume or bleed air constantly during operation. High air consumption is undesirable in certain applications such as when the fluid supply to the field instrument and the electropneumatic converter is process media like natural gas. For example, the costs associated with providing additional capacity in the fluid supply system can be substantial. Additionally, the constant bleed of such process media is both expensive and wasteful to the environment. Alternatively, current pulsed-mode electropneumatic converters are typically based upon either piezoelectric technologies or multiple solenoid configurations. Piezoelectric designs, such as known designs provided by Hoerbiger Gmbh of Altenstadt, Germany, may be extremely power consumptive and relatively expensive to implement. Further, piezoelectric designs are temperature limited due the fact that the piezoelectric effect begins to degrade below approximately −20 Celsius. Additionally, multiple solenoid designs are complex and can be expensive to manufacture due to replication of the electromagnetic circuit.